The present invention relates generally to a workpiece positioning devices. For a specific example, it may center a wafer that is within a range of sizes over a chuck. The workpiece, once precisely positioned, is ready for processing.
Workpiece positioning devices are well known in the art. One type of positioning device utilizes a centering ring that accepts different sized semiconductor wafers without changes to the system hardware. The wafer is placed in the centering ring and gravity urges the periphery of the wafer to slide along the walls of the centering ring to thereby center the wafer in the centering ring.
One problem with conventional centering rings is the use of stepped circles of different diameters that allow different sized wafers to fall into different sized concentric rings. Occasionally the wafer slides unevenly along the walls of the centering ring and gravity is insufficient to properly center the wafer within the concentric rings.
Another problem with centering rings is that foreign material, for example photo resist or flux used during the processing of a previous wafer, may cause the wafer to stick to the edges of the centering ring. This prevents the wafer from being accurately centered prior to processing.
Another problem with centering rings is that the centering ring typically has to swing into proper position for positioning the wafer and then must swing away from the processing station to allow for further processing of the wafer. This may causes particles to fall on the wafer prior to being processed.
Centering rings are particularly unsuited for wafers that require extreme accuracy, repeatability, reliability, and minimum particle generation. What is needed is a positioning device that accurately centers a wafer or other workpiece, is repeatable and reliable and produces a minimum amount of particles while avoiding the problems of the prior art.
The different embodiments of the invention may include one or more of the following objectives. One objective is to provide a workpiece positioning device that centers a workpiece that is within a range of sizes. All workpieces within the range may be centered without making modifications to the hardware of the positioning device.
Another object is to provide a positioning device that uses sensors/torque limitors to accurately center different sized workpieces without applying excessive pressure on the workpiece that might damage the workpiece.
Another object is to provide a positioning device that minimizes particle generation, particularly above the top surface of the workpiece.
Another object is to provide a positioning device that quickly centers the workpiece thereby improving the throughput of the processing station.
Another object is to provide a positioning device that may be used in combination with a variety of processing stations.
Another object is to center any semiconductor wafer that is within a range of sizes. All wafers within the range of sizes may be centered in a semiconductor processing station without modifying the positioning device. The positioning device is particularly useful for positioning semiconductor wafers larger than 50 mm in diameter.
The present invention provides a new positioning device that may be used with a range of workpiece sizes without modifying the hardware of the positioning device. The workpiece positioning device may includes a housing, a plurality of rotational shafts mounted from the housing extending generally in a vertical direction, a motor, a coupling mechanism coupling the motor to the plurality of rotational shafts, and a plurality of ring bars. A first end of each ring bar may be connected to one of the rotational shafts and each ring bar may extend generally in a horizontal direction. In a preferred embodiment, there are six (6) rotational shafts that are substantially equally spaced apart along a circumference of a circle. The ring bars extending from the rotational shafts may lay along the circumference of the circle.
Additional embodiments of the invention may include one or more of the following features. An alignment pin may be mounted on the distal end of one or more of the plurality of ring bars to assist in contacting the workpiece during the positioning process. A plurality of rest pins, preferably shorter and in front of the alignment pins, may also be mounted on the distal end of one or more of the plurality of ring bars to support the workpiece. A plurality of combination pins may be used instead of the rest and alignment pins. A torque limiter may be coupled to the motor to limit the amount of stress placed on the workpiece during the positioning process. Excessive stress might damage or destroy the workpiece.
The coupling mechanism for transferring motion generated by the motor to rotate the rotational shafts may take many different forms. Methods of transferring motion generated by a motor to a plurality of shafts are well known and particular embodiments of the invention may include these known methods. Non-limiting examples of some of the known methods include various configurations of levers, belt drive pulleys, pulley bearings, belts, and/or various configurations of gears.
The preferred coupling mechanism includes a plurality of belt drive pulleys, a plurality of pulley bearings, and a belt. The belt may be operably coupled to the motor, the plurality of belt drive pulleys, and the plurality of pulley bearings. Each belt drive pulley is preferably operably coupled to one of the rotation shafts. The motor is thus able to simultaneously rotate the plurality of rotation shafts in a clockwise direction or simultaneously rotate the plurality of rotation shafts in a counter-clockwise direction.
In operation, a workpiece may be centered over a particular location of a processing station by performing the following steps. The workpiece may be positioned with a robotic end effector above, and then placed on, a distal end for each of a plurality of ring bars. The workpiece is preferably rested on one or more rest pins attached to the distal end of the plurality of ring bars. A motor may simultaneously rotate a plurality of rotation shafts in a first direction, i.e. clockwise or counter-clockwise, thereby arcing the distal end for each of the plurality of ring bars towards the workpiece. This will result in the distal ends of the plurality of ring bars substantially uniformly urging the workpiece towards a particular location within the processing station. Alignment pins are preferably attached to the distal end of the ring bars and contact the workpiece during the urging of the workpiece. In a preferred embodiment, a dithering motion by the alignment pins at the end of the urging step may be used to improve the accuracy of the alignment procedure. In one embodiment of the invention, a chuck may be raised to accept, possibly by vacuum, a centered wafer. The ring bars may be removed from the processing station by rotating the plurality of rotation shafts in a second direction thereby arcing the distal end for each of the plurality of ring bars away from the workpiece. The workpiece may then be processed as it is centered on the chuck and the ring bars have been removed from the processing station. In a preferred embodiment, the processing station performs a flux spin coating process on a semiconductor wafer. After the workpiece en processed, the plurality of rotation shafts may be simultaneously rotated in the similar first direction again thereby arcing the distal end for each of the plurality of ring bars towards and below the workpiece. The chuck may lower and rest the workpiece on the rest pins. This allows space beneath the workpiece for an end effector to grip the workpiece, possibly by vacuum, and remove the workpiece from the processing station.
Another method for positioning a wafer in a processing station uses a plurality of combination pins mounted on a distal end of a plurality of ring bars. The combination pins may be arced inward to be below the wafer and the wafer lowered onto the combination pins, preferably by a robotic end effector. The end effector may be moved away from the processing station to allow a chuck to lift the wafer off the combination pins. The combination pins may be arced away from the wafer to give room for the chuck to lower the wafer to the same height as the combination pins. The combination pins may be arced toward the wafer so that the combination pins contact the edge of the wafer and urge the wafer toward a desired position. The combination pins may be arced away from the wafer and the processing station to allow for processing of the wafer. After the process, the chuck may raise the wafer and allow the combination pins to arc beneath the wafer. The chuck may lower the wafer onto the combination pins, thereby giving room for an end effector or other device to remove the wafer from the processing station.